Homeostasis Flashcards
What is homeostasis
maintenance of a constant internal environment. Mechanisms are in place to keep optimum conditions despite internal and external changes. This is needed for enzyme action and all cell functions.
What does homeostasis in the body control
Blood glucose concentration
Body temperature
Water levels
Which communications are involved in the automatic control systems
Nervous and hormonal communication
What do all control systems contain
Receptors - cells that detect stimuli (changes in the environment)
● Coordination centres - process the information received from the receptors, e.g. brain, spinal cord and pancreas
● Effectors - bring about responses to bring the conditions in the body back to optimum levels, e.g. muscles or glands
What is the usual nervous system like
Receptor cells convert a stimulus into an electrical impulse.
2. This electrical impulse travels along cells called sensory neurons to the central nervous system (CNS). 3. Here, the information is processed and the appropriate response is coordinated, resulting in an electrical impulse being sent along motor neurones to effectors.
4. The effectors carry out the response (this may be muscles contracting or glands secreting hormones).
What is a reflex action
an automatic (involuntary) and rapid response to a stimulu
How is the reflex arc different from the usual response of the nervous system
This pathway is different from the usual response to stimuli because the impulse does not pass through the conscious areas of your brain
What are the stages of the reflex arc
A stimulus is detected by receptors.
2. Impulses are sent along a sensory neuron.
3. In the CNS the impulse passes to a relay neuron.
4. Impulses are sent along a motor neuron.
5. The impulse reaches an effector resulting in the appropriate response
What are synapses and how do they work
Synapses are the gaps between two neurons.
● When the impulse reaches the end of the first neuron, a chemical(neurotransmitter0 is released into the synapse.
● This chemical diffuses across the synapse then bind with receptor molecules on the membrane of the second neuron.The receptor molecules on the second neuron can only bind to the specific neurotransmitters released from the first neuron.
● When the chemical reaches the second neuron, it triggers the impulse to begin again in the next neuron
What are the 5 components of the brain
Cerebral cortex
Medulla
Hypothalamus
Pituatry gland
cerebellum
What does the cerebral cortex do
controls consciousness, intelligence, memory and language; it is the outer part of the brain
What does cerebellum do
controls fine movement of muscles; rounded structure towards the bottom/back of brain
What does the medulla do
controls unconscious actions such as breathing and heart rate,; found in the brain stem in front of the cerebellum
Why is treating brain disorder difficult
It is complex and delicate ● It is easily damaged ● Drugs given to treat diseases cannot always reach the brain because of the membranes that surround it ● It is not fully understood which part of the brain does what
How can Neuroscientists map out the regions of the brain using 3 methods?
- Studying patients with brain damage Observing the changes in an individual following damage on a certain area of the brain can provide information on the role this area has.
- Electrically stimulating different parts of the brain done by pushing an electrode into the brain. The stimulation may result in a mental or physical change in the individual, providing information on the role this area of the brain has.
- Using MRI scanning techniques create an image of the brain. This can be used to show which part of the brain is affected by a tumour, or which part is active during a specific task.
What is the eye and what does it contain
Sense organ containing receptors sensitive to light intensity and colour
What is accomodation
Process of changing the shape of the lens to focus on near or distant objects
What does the retina do
Retina: Layer of light sensitive cells found at the back of the eye. When light hits this, the cells are stimulated. Impulses are sent to the brain, which interprets the information to create an image.
What are the two different types of receptor cells found in retina
cone cells- how we see light
Rod cells- How we see black and white
What does the fovea do
Hep produce the clearest image possible and contains only cone cells
What does the optic nerve do
- Optic nerve: A nerve that leaves the eye and leads to the brain. It carries the impulses from the retina to the brain to create an image.
What does the scelera do
- Sclera: White outer layer which supports the structures inside the eye. It is strong to prevent some damage to the eye.
What does the cornea do
The see-through layer at the front of the eye. It allows light through and the curved surface bends and focuses light onto the retina.
What does the iris do
Iris: Muscles that surround the pupil
contract or relax to alter the size of the pupil.
What do ciliary muscles do
contracts and relaxes to Hold the lens in place They control its shape.
What do suspensory ligaments do
tighten and slacken to Hold the lens in place They control its shape.
How does the iris respond to bright light
the circular muscles contract and radial muscles relax to make the pupil smaller- avoiding damage to the retina
How does the iris respond to dim light
circular muscles relax and the radial muscles contract to make the pupil larger- so more light can enter to create a better image.
How do we focus on near objects
The ciliary muscles contract
The suspensory ligaments loosen
The lens is then thicker and more curved- this refracts the light more
How do we focus on distant objects
● The ciliary muscles relax
● The suspensory ligaments tighten
● The lens then becomes thinner- light is refracted less
What are the two common eye defects and how do they work
Myopia-short sightedness,rays of light focus in front of retine beause lens is too curved
Hyperopia- long sightedness, rays of light focus behind the retina because lens is too flat
How is myopia corrected
using concave lens
How is hyperopia corrected
using convex lenses
What are the treatments of eye defects
spectacle lenses- concave lenses to spread out the light to treat myopia and convex lenses to bring the rays together to treat hyperopia
● Contact lenses- work in the same way as glasses but allow activities such as sport to be carried out, hard or soft contact lenses last for different lengths of time
● Laser eye surgery- lasers can be used to either reduce the thickness of the cornea (so it refracts light less) to treat myopia or change its curvature (so it refracts light more strongly) to treat hyperopia
● Replacement lens- Hyperopia can be treated by replacing the lens with an artificial one made of clear plastic (or adding the plastic on top of the natural lens). The risks include damage to retina or cataracts developing.
What is the thermoregulatory centre
monitors and controls body temperature is found in the brain.
● Has receptors that monitor the temperature of the blood
● Has receptors in the skin that send impulses to the thermoregulatory centre
What happens if the body temperature is too cold
We conserve heat as well as producing more.
Blood vessels constrict(vasoconstriction)-so less blood flows near surface and less heat energy is lost
Erector muscles contract -hairs stand on end to create an insulating layer, trapping warm
Skeletal muscles contract rapidly (shivering) to generate heat required from respiration-heat energy is produced as waste
Sweating stops
What happens if the body temperature is too high
Blood vessels expand-vasodilation)- so more heat energy is transferred to surrounding because lots of warm blood is passing close to skin surface
Sweat produced from sweat glands and as t evaporates it takes energy away with it
What is the endocrine system
composed of glands that secrets hormones into the bloodstream
blood carries hormones to target organs to carry out a response
compared to the nervous system it is slower but effects last longer
What is the pituitary gland
Master gland
Secretes hormones into the blood to either have an effect on the body or act on other glands to stimulate them to produce different hormones
What does the pancreas do
Secretes insulin
Controls blood glucose levels
What does thyroid gland do
secretes thyroxine
Controls metabolic rate, heart rate and temperature
Important for growth and development
levels controlled by negative feedback loop- pituitary gland releases tsh if thyroxine levels are too low
What does adrenal gland do
Secretes adrenaline
Involved in the ‘fight or flight’ response (the body’s response to stressful situations)
Increases heart rate
Boosts delivery of oxygen and glucose to brain and muscles
What do ovaries do
Secretes oestrogen
involved in the menstrual cycle and the development of female secondary sexual characteristics (different features that develop during puberty that distinguish a female from a male)
What do testes do
Secretes testosterone-stimulates sperm production
Is involved in the production of sperm and the development of male secondary sexual characteristics
How do glucagon and insulin act in a negative feedback loop
If the glucose levels are too high, the pancreas produces the hormone insulin
Insulin binds to cell in target organs (muscles and liver) causing:
1) Glucose to move from the blood into muscle cells for respiration
2) Excess glucose to be converted into glycogen which is stored in the liver -The blood glucose concentration is reduced
Rigorous activity, glucose for respiration and therefore there is less in the blood.
If glucose levels decrease, the pancreas produces the hormone glucagon
Glucagon binds to to the liver cells causing glycogen to be broken down into glucose
Glucose is released into the blood, increasing the blood glucose concentration
What is type 1 diabetes and how is it treated
the pancreas cannot produce enough insulin ● Blood glucose level can rise to a fatal amount ● Glucose is excreted with urine and lots of urine is produced leaving the individual very thirsty ● It is treated with insulin injections at meal times, which results in glucose being taken up from the bloodstream ● It is also advised to limit the intake of simple carbohydrates which contain lots of glucose ● Doctors are attempting to cure diabetes with pancreas and pancreatic cell transplants, and genetically engineering pancreatic cells from mice to make insulin
What is type 2 diabetes and how is it treated
the body cells no longer respond to insulin ● Blood glucose levels can rise to a fatal amount ● Obesity is a risk factor for this disease ● Treatments include reducing the number of simple carbohydrates in diet, losing weight and increasing exercise ● There are also drugs to make insulin more effective on body cells, help the pancreas make more insulin or reduce the amount of glucose absorbed from the gut
How does too much or too little water cause cells not to function properly
If the water concentration of the blood increases then cells in the body take up water. ● This is because the concentration of water in the bloodstream is higher than the concentration of water in the cells, so water moves into the cells by osmosis. ● Cells then expand as they take up more water, and may eventually burst
● If the water concentration of the blood decreases then cells in the body lose water. ● This is because the concentration of water in the bloodstream is lower than the concentration of water in the cells, so water moves out of the cells by osmosis. ● Cells shrink as they lose water.
What are kidneys important for and how do they make urine
The kidneys are very important in maintaining the balance of water and other substances in the body. As blood moves through the body, it makes urine by:
● Filtering out the waste products
● Selectively reabsorbing useful substances such as glucose, ions and water
What are the three waste products
Water,ions,urea
How is water a waste product
Can also leave the body at the lungs as a result of exhalation, or from the skin in sweat (there is no control over the amount lost)
● Depending on the concentration of water in the blood, a certain amount of water is lost as urine
How are ions a waste product
They are taken into the body via food ● If the ion concentration is incorrect, then too little or too much water may enter body cells. This is because the water potential of the blood would be altered ● They are lost in sweat (there is no control over the amount lost) ● In the kidneys, certain amounts of ions are reabsorbed into the blood after it has been filtered to ensure the concentration in the blood is maintained
How is urea a waste products
Amino acids are the products of the digestion of proteins. Amino acids are deaminated in the liver to form ammonia. As ammonia is toxic it is converted to urea so it is safe for excretion
● It is lost in sweat (there is no control over the amount lost)
● In the kidneys, it is filtered out of the blood
What is ADH
Anti diuretic hormone-involved in the control of the loss of water as urine.
It is released into the pancreas by the pituitary gland when a receptor in the brain detects that the blood is too concentrated.
What happens if the water concentration is too low
More ADH is released by the pituitary gland
Kidney tubules reabsorb more water
Little urine is produced
What happens if the water concentration is too high
Less ADH is released by pituitary gland
Kidney tubules reabsorb less water
More urine is produced
What is kidney failure
when your kidneys stop working. This means waste products build up which can be harmful to the body, and eventually results in death.
What are the two ways to treat people with kidney failure
Dialysis
Transplant
How does kidney dialysis work
the function of the kidneys is carried out using an artificial membrane ● Blood moves between partially permeable membranes surrounded by dialysis fluid (has the same concentrations of ions and glucose as healthy blood). ● Useful ions and glucose are not lost from the blood but urea, excess ions and water diffuse across the membrane.
How does kidney transplant work
Kidney transplants: providing the individual with a healthy kidney ● This is currently the only cure. ● They are transplanted from people who have died suddenly, or from people still alive ● They mean that the person does not need to visit the hospital as regularly as they did when undergoing dialysis, and it is cheaper than the overall cost of dialysis. ● The main problem is that they could be rejected from the body as a result of the immune system recognising the antigens on the donor organ as foreign. The chance of this happening can be reduced by using immunosuppressant drugs. ● However, this means that the person can be left vulnerable to other diseases. In addition, transplanted kidneys do not last forever
What are the advantages and disadvantages of dialysis
Advantages- No shortage of dialysis machines
Diadantages-has to be done three times a week, with the process itself taking three to four hours.
It acts as an artificial kidney and keeps people alive while they wait for a transplant.
possibility of blood clots forming,
amount of time it takes
have to follow a strict diet
It is also an unpleasant experience, and the build up of waste products between sessions can leave you feeling ill
Expensive in long term
What are the advantages and disadvantages of kidney transplant
Advatages:person does not need to visit the hospital as regularly
Allows patient to live a normal life
cheaper than the overall cost of dialysis.
Disadvantages:
could be rejected from the body as a result of the immune system recognising the antigens on the donor organ as foreign.
Patients have to use immunosuppressant drugs for the rest of their life.
person can be left vulnerable to other diseases. In addition
transplanted kidneys do not last forever
Shortage of kidney donors
What happens during puberty
Reproductive hormones cause the secondary sex characteristics to develop
What us the male reproductive hormone and what does it do
testosterone. ● Produced by the testes
● Stimulates sperm production
What is the female reproductive hormone and what does it do
oestrogen
● Produced in the ovary
● Produces physical changes and is involved in the menstrual cycle
What is the menstrual cycle
Process the body undergoes each month to prepare for a potential pregnancy. It begins with the lining of the uterus breaking down, and the woman has her period(menstruation). The layer then builds up again, until ovulation (day 14) occurs- an egg is released from the ovary and moves to the uterus via the fallopian tube. If a fertilised egg has not been embedded in the lining after 28 days, it begins to break down and the cycle continues.
What is FSH
Follicle stimulating hormone (FSH)
causes the maturation of an egg in the ovary, within a structure called a follicle
Produced in the pituitary gland
Stimulates the ovaries to produce oestrogen
What is LH
Luteinising hormone (LH)
Produced in the pituitary gland
Produced as a result of the hormone oestrogen
Stimulates the release of the mature eggs from ovaries (ovulation)
What does oestrogen do
Causes the lining of the uterus to thicken again Produced in the ovaries
Secreted as a result of FSH
Stimulates the production of LH and inhibits the secretion of more FSH
What does progesterone do
Produced in the ovaries and secreted from the egg follicle.
Maintains the lining of the uterus, and supports a pregnancy if the egg is fertilized
Inhibits the release of both FSH and LH
What are all the methods of hormonal contraception
Conctraceptive pill
Contraceptive patch
Contraceptive implant
Contraceptive injection
Intrauterine devices
How do contraceptive pills work
The mixed pill contains oestrogen and progesterone ○ This means the oestrogen levels are constantly high, inhibiting FSH so no eggs mature. ○ The lining also stops developing and the mucus in the cervix becomes thick so sperm cannot move through ○ Some possible side effects include changes in mood, mood swings, depression, breast pain or tenderness, breast enlargement, increased blood pressure, headaches,nausea
● The progesterone only pill ○ This has less side effects in comparison to the mixed pill.
How do contraceptive patches work and for how long
The contraceptive patch contains oestrogen and progesterone. ● It is small and is stuck on the skin ● Lasts for one week The contraceptive implant releases a continuous amount of progesterone. ● This prevents the ovaries from releasing the egg, thickens the mucus in cervix so sperm cannot swim and stops fertilised eggs from embedding in the uterus ● Lasts for three years The contraceptive injection is made up of progesterone. ● Same effect as the implant ● Lasts for 2 to 3 months The plastic intrauterine device (IUD) releases progesterone. ● Same effect as the implant ● T shaped, inserted into the uterus
How do contraceptive implant work and for how long
contraceptive implant releases a continuous amount of progesterone.
this prevents the ovaries from releasing the egg, thickens the mucus in cervix so sperm cannot swim and stops fertilised eggs from embedding in the uterus Lasts for three years
How does contraceptive injection work and for how long
made up of progesterone.
Same effect as the implant
Lasts for 2 to 3 months
How do plastic intrauterine devices work and for how long
releases progesterone.
Same effect as the implant
T shaped, inserted into the uterus
Last 3+ years
What are the non-hormonal contraceptions (these stop sperm fertilising the egg)
spermicides
Barrier methods condoms and diaphragms:
The copper intrauterine device
Surgical methods of male and female sterilization
Abstaining from intercourse ensures that an egg is not fertilized. Others may only abstain during ovulation.
How do barrier methods work
include condoms and diaphragms: ● Condoms are either worn over the penis or are inside the vagina. They also prevent the individual from contracting sexually transmitted diseases. A problem is that it can tear and therefore let sperm through.
diaphragm is a plastic cup which is positioned over the cervix. It is used with spermicide.
How do spermicides work
These kill or disable sperm, but are only 70% to 80% effective.
how does the copper intrauterine device work
killing sperm in the uterus and stopping any fertilised embryos from implanting in the uterus lining.
How do surgical methods work and what do they involve
Surgical methods of male and female sterilization involve cutting and tying the fallopian tubes or sperm duct. This lasts forever.
How does abstaining from intercourse work
ensures that an egg is not fertilised. Others may only abstain during ovulation.
How can infertility be treated
Fertility drugs are used to increase the chance of pregnancy. ● The main hormones used are FSH and LH because they stimulate the maturation and release of the egg. ● The woman can then become pregnant normally. In Vitro Fertilisation (IVF) is another treatment. ● The mother is given FSH and LH to encourage the maturation eggs ● These are extracted from the mother and fertilised in the lab using sperm ● The fertilised eggs develop into embryos and then one or two are inserted in the uteru
How do fertility drugs work
● The main hormones used are FSH and LH because they stimulate the maturation and release of the egg. ● The woman can then become pregnant normally.
How does IVF work
The mother is given FSH and LH to encourage the maturation eggs
These are extracted from the mother and fertilised in the lab using sperm from the father
The fertilised eggs develop into embryos and then one or two are inserted in the uteru
What is one benefit of IVF
What are the negatives of IVF
It is physically stressful as women may have reactions to the hormones, such as feeling sick.
It is emotionally stressful because it may not work- success rate for IVF is 26%.
It can lead to multiple births unexpected and may be a risk to the babies and the mother
Can be expensive if the process needs to be repeated.
Ethical issues- Unused embryos are destroyed
What does thyroxine do
regulates basal metabolic rate (how quickly reactions occur). It is also important in growth and development.
The levels of thyroxine are controlled by negative feedback. ● When the levels increase, it is detected by receptors in the brain ● This inhibits the release of TSH ● This inhibits the release of thyroxine, so levels fall
Where is thyroxine released and what is the release stimulated by
Released by the thyroid gland ● Its release is stimulated by the thyroid stimulating hormone
How is the production of thyroxine regulated?
The pituitary gland produces Thyroid Stimulating Hormone (TSH), which stimulates the thyroid gland to produce thyroxine.
Thyroxine then inhibits the production of TSH from the pituitary gland.
How is thyroxine an example of negative feedback
If thyroxine levels are too low - the pituitary gland will release TSH. This then stimulates the thyroid gland to release more thyroxine. So thyroxine levels in the blood increase back up to normal.
If thyroxine levels are too high - the thyroxine will inhibit the pituitary gland from producing TSH. Less TSH means that the thyroid gland won’t release as much thyroxine. So thyroxine levels in the blood fall back to normal
What is adrenline and what does it stimulate
produced in times of stress, and stimulates the ‘fight or flight’ response
where is adrenal released and what causes it to be released
Released by the adrenal glands (on top of the kidneys) ● This is stimulated by fear or stress, detected in the brain
What are the effects of adrenaline
Increased heart rate and breathing rate to deliver more oxygen and glucose to the brain and muscles for respiration ○ Glycogen stored in liver is converted to glucose for respiration ○ Pupils dilate to let in more light ○ Blood flow to muscles is increased ○ Blood flow to digestive system is decreased
What are the 2 tropisms in plants and what are they responses to
Phototropism-response to light
Geotropism/Gravitropism- response to gravity
How do plants show positive phototropism
The plant is exposed to light on one side.
Auxin, a hormone, moves to the shaded side of the shoot.
Auxin stimulates cells to grow more here.
This means the shoot bends towards the light.
The plant receives more light, meaning photosynthesis can occur at a faster rate.
How do most shoots show negative geotropism
Auxin moves to the lower side.
The cells of the shoot grow more on the side with most auxin, so it stimulates cells to grow more here.
This makes the shoot bend and grow away from the ground.
This is beneficial as light levels are likely to be higher further away from the ground
How do most root show positive geotropism
they grow towards gravity
If a root is horizontal:
● Auxin moves to the lower side.
● The cells of the root grow more on the side with less auxin, so it stimulates cells to grow on the upper side.
● This makes the root bend and grow downwards.
● This is beneficial as there are more likely to be increased levels of water and nutrients lower down, and it provides stability for the plant.
What happens when auxin distribution becomes equal on both sides
It grows straight in that direction
What does Unequal distributions of auxin cause
unequal growth rates in plant roots and shoots
How can you investigate the effect of light or gravity on newly germinated seedlings
by varying conditions.
● Placing in cardboard box and shining light from one side
● Attaching a petri dish containing the seedlings to a wall (effects of gravity)
What is the function of gibberlins
important in initiating seed germination.
What is the function of ethene
controls cell division and ripening of fruits.
What are the uses of auxins
As weed killers
● Many weeds are broad-leaved
● Weedkillers, containing auxin, have been synthesised so they only affect broad-leaved plants
● The increased amount of auxin causes the cells to grow too rapidly ● This results in the weed dying
- As rooting powders
● Plants with desirable features are cloned to make more plants with the same feature
● One way to clone a plant is to take a cutting from the original plant
● Rooting powder containing auxin is applied to it and it is placed in the ground
● Roots grow and the new plant begins to grow very quickly - To promote growth in tissue culture
● Another way to clone a plant is to use tissue culture
● Cells from the plant are taken are placed in a growth medium containing lots of nutrients
● Hormones such as auxins are added
● The cells begin to form roots and shoots
What is the use of ethene
controls ripening, it is used in the food industry.
● Fruit is picked when it is not ripe
● It is firm which means that during transport it gets less bruised and damaged
● When it is needed to be sold, it is exposed to ethene and warmer temperatures
● Ethene is involved in controlling cell division and stimulates enzymes that result in fruit ripening.
● This reduces wastage as more fruit is suitable to be sold and it does not ripen too early
What is the use of gibberelins
Gibberellins are used for:
1. Ending seed dormancy ● In the brewing industry, the germination rate of barley seeds is increased to make malt.
2. Promoting flowering ● Instead of requiring certain conditions such as longer days and low temperatures to flower, applying this hormone allows it to flower in any conditions and with bigger flowers.
3. Increasing fruit size ● The seeds in fruit produce gibberellins to increase fruit size. ● This means that seedless fruit is generally smaller. ● Seedless fruit can be sprayed with gibberellins to increase their size
